This invention relates to the conversion of energy from naturally occurring sources of mechanical energy, such as the mechanical energy present in ocean surface waves or current flow in water, streams and air, to electrical energy and, in particular, to the efficient production and transfer of electric energy.
Various wave energy converter (WEC) systems are known. For example, reference is made to U.S. patent application Ser. No. 09/379,421 filed Aug. 21, 1999, titled “Wave Energy Converter Utilizing Pressure Difference”, assigned to the assignee of the present application and the teachings of which are incorporated herein by reference.
Numerous problems exist in the design of a mechanical system for harnessing the energy contained in ocean waves. Particularly, a problem exists in harnessing this energy efficiently. To begin with, there is a problem in converting wave energy to usable mechanical motion and force. In addition, there is a further problem of converting the mechanical energy into electrical energy in an efficient manner. A significant difficulty in increasing the efficiency of converting the ocean wave energy into electric energy is due to the fact that the waves vary continuously in amplitude, frequency and phase as a function of time.
Various concepts have been proposed to try to increase the efficiency of converting wave energy to electric energy using WECs. In some of these systems, the mechanical components of the WECs are “tuned” to have a high efficiency when operating with ocean waves of a specific frequency. Given the narrowband behavior of these systems and the highly variable nature of ocean waves, the overall efficiencies of such systems are poor.
It has also been proposed to adjust the mechanical properties of the WEC to take into account the predominant wave frequency over a period of time. Incorporating such a proposal requires mechanical devices that change the spring, mass and damping properties of the WEC. However, to effectuate the called for proposed adjustments to the mechanical properties of a WEC is problematic since there is no practical way to provide continuous, or multiple level, tuning of the system.
Another scheme for increasing the efficiency of a WEC is shown in U.S. Pat. No. 6,731,019, based on application Ser. No. 09/922,877 filed Aug. 6, 2001 titled “Apparatus and Method for Optimizing the Power Transfer Produced by a Wave Energy Converter (WEC)” assigned to the assignee of the present application and the teachings of which are incorporated herein by reference. In this patented system, the electromechanical device is controlled and its mechanical behavior is altered to increase its energy conversion efficiency by tuning the output load.
In all of the known proposed wave energy converter efficiency-boosting schemes, the energy storage and/or tuning components are large and/or expensive making it difficult and/or expensive to produce commercially viable products. In addition, the known systems tend to be reactive (i.e., do not anticipate certain wave conditions) and pro-active control over the behavior of the WEC.